Within the current domestic cellular telephone industry, there exists substantial economic and consumer pressure to reduce the physical size of hand held, cellular telephone units. Consequently, cellular telephone manufacturers tout the small size and light weight of their products, and are constantly striving to improve upon the material and mechanical efficiency of their designs.
Domestic manufacturers have capitalized on and taken advantage of a number of design aspects which have led to the relatively rapid appearance of smaller and thinner cellular phone units. However, in many cases, these designs have begun to reach the point where structural members such as the frame and plastic case enclosures are significant components of the overall thickness of the phone unit. For this reason, another strategy for implementing size and weight reduction involves minimization of the structural components. Unfortunately, in practice, it is difficult to remove thickness from the structural members of the phone without adversely affecting strength and reliability of the unit.
In the past, the problem of structural minimization has been approached by gradually reducing wall thickness in the plastic and metal structural components. However, current phone designs are already reaching the limits of existing thin wall technology. For example, the next generation phone designs currently under consideration will require a structural frame thickness on the order of 1.0 millimeter and a plastic component wall thickness of roughly 0.8 millimeters. Any further reduction in overall phone thickness would require local reductions in wall thickness to allow tall components such as IF filters to recess into a pocket formed in the frame or plastic case enclosure. Those skilled in the art will appreciate that magnesium and magnesium alloys are some of the most common materials used in structural frame members associated with cellular telephone units. In frames fabricated utilizing die-cast production techniques, wall thickness reduction is typically accomplished by switching from magnesium alloys to zinc or zinc alloys. However, there is a substantial weight penalty associated with zinc and its alloys which generally makes their use unattractive.
In general, thin wall components are very difficult to mold without cosmetic blemishes and tend to lack structural integrity due to the difficulties associated with maintaining the melt at sufficiently high temperatures as the part is molded or cast. Adding pockets of locally reduced wall thickness only serves to compound an already difficult problem. Furthermore, the inclusion of such pockets rigidly and absolutely fixes the location of the components which must be recessed within them, thus making future circuit board changes very costly to implement. Having local pockets also generally complicates any attempts to utilize the component across multiple systems or designs. That is, a pocketed, plastic enclosure case designed to accommodate tall components for a particular cellular phone model will probably not be easily utilized on a different phone model.
Therefore, there is and continues to be a need for a practical approach to further minimizing the size and weight of cellular telephone structural components beyond the limitations imposed by the thin wall fabrication techniques currently employed in the cellular telephone industry.